The present invention relates generally to fasteners and more particularly to two part fasteners of the type comprising a headed pin adapted to have a collar swaged thereon by action of a pulling tool gripping grooves on a minimum length pintail portion of the pin and more especially a pin constructed of an exotic material such as a titanium alloy or the like, and having a pintail portion of minimum length.
Two part fasteners employing a headed pin which are adapted to have a collar swaged to a shank portion thereof by means of a pulling tool gripping pull grooves in a pintail portion of the pin are well known in the art. Typically, such pins are provided with an elongated shank on which are provided successively from the head axially outwardly a plurality of lock grooves into which the collar is swaged, a breakneck groove, and a pintail portion having a plurality of pulling grooves. These fasteners are designed to be set by a pulling tool engaging the pulling grooves so as to exert an axial tension on the pin to secure a plurality of workpieces together and thereafter cause an anvil provided on the tool to swage the collar into locking engagement with the lock grooves. Thereafter, the breakneck groove operates to enable the tool to separate the pintail from the set fastener. In tools conventionally used in setting these fasteners, the severed pintail is not ejected forwardly therefrom but rather is moved axially through the tool jaws by the pintail of the next fastener to be set and is ejected to the rear of the tool. It is a common practice to form various ones of the grooves in the pin by rolling. In the process of rolling the metal displaced to form grooves is moved to define crests; normally then a pin blank of nominal diameter, i.e. between the crest and root diameter is used. Thus when the grooves are rolled a land of nominal diameter remains. With some materials the breakneck groove is rolled providing a rollback land of a diameter approximating the diameter of the crest of the pull grooves and/or locking grooves. With titanium alloys it is a practice not to roll the breakneck groove but to machine the same. Whether the breakneck groove is formed by rolling and an increased diameter rollback land is formed or the breakneck groove is machined from a blank (rolled to form locking and pull grooves) of a nominal diameter, the rollback land (or area adjacent the breakneck groove) poses a problem in minimizing the length of the pintail portion. Thus conventional pintails have a smooth shank portion or rollback land immediately adjacent the breakneck groove which is of a diameter equal to or greater than the nominal diameter of the pull grooves. With such a construction, it has been necessary to provide a sufficiently long pintail to insure that the previously separated pintail completely clears the jaws of the tool since the rollback (or nominal diameter) land if located in the jaws will hold them open and prevent gripping or full gripping of the next fastener. Since the severed pintail is discarded, this extra length requirement results in needless extra cost of materials for the fastener which costs become quite significant in such fasteners fabricated from exotic metals such as titanium alloys of the like.
Accordingly, the present invention provides a fastener in which the diameter of the smooth shank portion or rollback land of the pintail is reduced to be no greater than the root diameter of the pull grooves. This thereby enables the jaws of the pulling tool to fully engage the pull grooves of the next fastener to be set without regard to whether the previously separated pintail has fully cleared the jaws or not. This diameter reduction allows substantial cost savings to be realized in reduced material requirements as the pintails need be only long enough to accommodate the minimum number of pull grooves required for the particular type fastener while still enabling the fastener to be installed with conventional tools presently in use.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.